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Hello, I am solving for multiphase flow in porous media.. which couples 2 physics- darcy law and phase transport in porous media.. I have to solve for two saturations and two pressures in two phases. I have also introduced coeffiecient form ode to solve heat transfer. After computation, I am getting theses errors- What is wrong I am doing can anyone explain?

Attempt to evaluate negative power of zero. - Function: ^ Failed to evaluate temporary symbolic derivative variable. - Variable: comp1.dl.U@VDN$comp1.pgX - Defined as: (0.5*((comp1.dl.ul1^2)^(-0.5)))*((comp1.dl.ul1*2)*(-comp1.dl.Tra11)) Failed to evaluate temporary symbolic derivative variable. - Variable: comp1.beta@VDN$comp1.pgX - Defined as: ((comp1.dl.rho*Cpg)+(rhow*Cpw))*((0.5*((comp1.dl.ul1^2)^(-0.5)))*((comp1.dl.ul1*2)*(-comp1.dl.Tra11))) Failed to evaluate expression. - Expression: (-((comp1.Tx*(((comp1.dl.rho*Cpg)+(rhow*Cpw))*((0.5*((comp1.dl.ul1^2)^(-0.5)))*((comp1.dl.ul1*2)*(-comp1.dl.Tra11)))))-(-(d(comp1.pg,x)*(sigmag*(comp1.dl.rho*((0.5*((comp1.dl.ul1^2)^(-0.5)))*((comp1.dl.ul1*2)*(-comp1.dl.Tra11)))))))))*dvol_spatial Failed to evaluate Jacobian of expression. - Expression: (-(((comp1.da*comp1.Tt)+(comp1.beta*\comp1.Tx))-comp1.f))*dvol_spatial Failed to evaluate Jacobian of expression. - Expression: (-(comp1.da*comp1.Tt+comp1.beta*comp1.Tx-comp1.f)*test(comp1.T)-lambda*comp1.Tx*test(comp1.Tx))*(dvol_spatial)